Variable rate coding for enabling high performance communication

ABSTRACT

A protocol for optimizing the use of coded transmissions such as over wireless links. In this technique, interframes are split into segments selected to be an optimum size according to transmission characteristics of the radio channel. The inverse process is applied at the receiver. Using this scheme, segments containing erroneous data may be resent.

CLAIM OF PRIORITY

This continuation application is related to, and claims priority to, thenon-provisional U.S. Utility Patent Application entitled “VARIABLE RATECODING FOR ENABLING HIGH PERFORMANCE COMMUNICATION,” filed Apr. 9, 2013,having an application Ser. No. 13/859,254, and Attorney Docket Number42P50308C4; this continuation application is related to, and claimspriority to, the non-provisional U.S. Utility Patent Applicationentitled “VARIABLE RATE CODING FOR ENABLING HIGH PERFORMANCECOMMUNICATION,” filed Oct. 28, 2011, having an application Ser. No.13/284,070, which issued as U.S. Pat. No. 8,437,329 on May 7, 2013,having Attorney Docket No. 42P50308C3; this continuation application isrelated to, and claims priority to, the non-provisional U.S. UtilityPatent Application entitled “VARIABLE RATE CODING FOR ENABLING HIGHPERFORMANCE COMMUNICATION,” filed Nov. 1, 2010, having an applicationSer. No. 12/917,008, which issued as U.S. Pat. No. 8,068,474 on Nov. 29,2011, having Attorney Docket No. 42P50308C2; this continuationapplication is related to, and claims priority to, the non-provisionalU.S. Utility Patent Application entitled “VARIABLE RATE CODING FORENABLING HIGH PERFORMANCE COMMUNICATION,” filed Sep. 21, 2009, having anapplication Ser. No. 12/563,466, which issued as U.S. Pat. No. 7,826,437on Nov. 2, 2010, having Attorney Docket No. 42P50308C; and thiscontinuation application is related to, and claims priority to, thenon-provisional U.S. Utility Patent Application entitled “VARIABLE RATEFORWARD ERROR CORRECTION FOR ENABLING HIGH PERFORMANCE COMMUNICATION,”filed Mar. 5, 1999, having an application Ser. No. 09/263,358, whichissued as U.S. Pat. No. 7,593,380 on Sep. 22, 2009, having AttorneyDocket No. 42P50308, the entire contents of each being incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The widespread availability of personal computers at low cost has led toa situation where the public demands access to the Internet and othercomputer networks at the lowest possible cost. This demand is beingtransferred to the need to also provide network access for portabledevices such as laptop computers, personal digital assistants, and thelike. Users of such portable devices even now expect to be able toaccess such computer networks with the same convenience that they havegrown accustomed to when using wire line connections.

Unfortunately, there is still no widely available satisfactory solutionfor providing low cost wireless access to the Internet at high speed. Atthe present time, the users of wireless modems that operate with theexisting cellular telephone network often experience a difficult timewhen trying to, for example, view Web pages. This is at least in partdue to the fact that the architecture of cellular telephone networks wasoriginally designed to support voice communication and not thepacket-oriented data communication protocols in use for the Internet. Inaddition, the protocols used for connecting users of wide area networksdo not lend themselves to efficient transmission over wirelessinterfaces.

Certain protocols have been proposed that provide multiple data linksover a wireless communication system such as one that uses code divisionmultiple access (CDMA). For example, one such system was described inour co-pending United States patent application entitled “A ProtocolConversion and Bandwidth Reduction Technique Providing Multiple nB+DISDN Basic Rate Interface Links Over a Wireless Code Division MultipleAccess Communication System,” Ser. No. 08/992,759 filed Dec. 17, 1997and assigned to Tantivy Communications, Inc., the assignee of thepresent application. With such techniques, high speed data service canbe provided over digital cellular connections through a more efficientallocation of access to the wireless channels. In particular, a numberof sub-channels are defined within a standard CDMA channel bandwidth,such as by assigning a different code to each sub-channel. Theinstantaneous bandwidth needs of a given connection are then met bydynamically allocating multiple sub-channels on an as-needed basis foreach session. For example, sub-channels can be granted during times whenthe subscriber bandwidth requirements are relatively high, such as whendownloading Web pages. The bandwidth is then released during times whenthe content is relatively light, such as when the user is reading apreviously downloaded Web page.

However, to implement such a system requires careful planning of variousmodulation and coding schemes in order to accomplish the maximumpossible bit rate while minimizing the effects of noise, multipath, andother sources of errors. For example, modulation codes and pseudorandomspreading codes must be carefully selected to minimize interferenceamong channels occupying the same radio frequency carrier. In addition,it is necessary for framing bits to be inserted in data streams so thathigher layered data protocols such as transmission controlprotocol/Internet protocol (TCP/IP) communication can take place.

SUMMARY OF THE INVENTION Statement of the Problem

While the above-mentioned systems work well in relatively noise-freeenvironments, they are not optimal in certain respects.

For example, although a cyclic redundancy check (CRC) error can indicatethat a TCP/IP frame is received in error, use of a CRC is not optimum inthat reception of an erroneous frame requires retransmission of theentire frame. Unfortunately, access techniques which requireretransmission are particularly troublesome in shared access wirelessenvironments such as CDMA where access must be specifically granted toaccommodate the retransmission. For example, in CDMA systems, the errorscan actually have a non-linear effect, reducing system capacity by anamount which is greater than the retransmission bandwidth. It istherefore desirable to minimize the need to retransmit data as much aspossible.

Certain techniques known as forward error correction (FEC) are generallyused with CDMA and other multiple access modulation schemes applied tovoice transmission. Such techniques accept a group of bits, or “block,”to be sent over a wireless channel and then, according to sophisticatedmathematical algorithms, determine values for additional redundant bits.The number of redundant bits may be quite significant. For example, itis common to use so-called one-half rate, one-third rate, or evenone-quarter rate codes whereby the number of bits in a block actuallytransmitted increases by a factor of two three, or four respectively.

The forward error correcting code can therefore be used to not onlydetect that a particular string of bits has been received in error, butalso to implement error correction. This eliminates the need toretransmit an entire packet due to an error in one or more bits. Forwarderror correction has thus been widely used in implementations such assatellite broadcast where retransmission is impractical and/orexpensive.

Unfortunately, implementation of forward error correction leads to loweroverall throughput as measured by the number of packets transmitted permegahertz of available channel bandwidth. In addition, the need toobtain the best error performance typically dictates that a relativelylarge block size be used for the highest performance algorithms.Implementation of such error correction algorithms therefore incurslatencies in that the entire block must be available at the receiverbefore it can be decoded. In addition, if an error is detected whichcannot be recovered through the forward error correction process,additional latencies are incurred while the block is retransmitted.

DETAILED DESCRIPTION

The present invention is implemented using a protocol converter disposedbetween the physical communication layers, such as may be associatedwith implementing a wireless communication protocol, and a networklayer, such as may be associated with implementing a networkcommunications protocol.

Briefly, in the present invention, the protocol converter on thetransmitter side first splits a network layer frame, such as a TCP/IPframe, into smaller portions referred to as segments. The segment sizeis variable in length according to an observed error rate. A minimumsegment size, for example, is two bytes and a maximum segment size is512 bytes in a preferred embodiment. All segments across a frame areequal in size.

Information is then added to each of the segments to permit theirreassembly into the frame at the receiver. In particular, a segmentposition number is added to permit the segment to be placed into theproper position when reconstructing the network layer frame at thereceiver.

At this point, the segments are arranged into groups referred to hereinas blocks. A forward error correction (FEC) algorithm is then applied tothe block as a whole. In a preferred embodiment, a block contains 1331information bits. Therefore, using a one-third rate code, the FECencoding process provides an output FEC block of 4096 bits.

The protocol also preferably makes use of multiple physical layerconnections referred to herein as sub-channels to transmit the encodedFEC blocks at an overall desired transmission rate. The FEC block isthen split among the allocated sub-channels such as on a bit-by-bitbasis. The bits comprising the FEC block are then sent over thesub-channels. In this case, a link sequence identifier may typicallyalso be added to identify the order in which the outgoing blocks aresent over the sub-channels.

On the receiver side, which in effect includes a protocol converter thatperforms the inverse function, bits received over the varioussub-channels are first assembled into an FEC block. The FEC block, inthe preferred embodiment as a block of 4096 bits, are then presented tothe inverse FEC algorithm to strip off the redundant code bits andperform error correction.

The output of the FEC decoding process is then split into segments. Thecyclic redundancy check information within each segment is then comparedto determine whether a particular segment was received in error. If thisis the case, then a request is made to retransmit the erroneouslyreceived segment.

Eventually, the received segments are reassembled into a completenetwork layer frame.

The protocol converters at both the transmitter and receiver ends mayalso dynamically adjust the size of the segments based upon an observedreceived segment error rate in order to optimize overall throughput. Forexample, at the receiver side, a segment with the bad cyclic redundancycheck (CRC) is discarded and counted as a “bad” segment. By keepingtrack of the sequence numbers of the received segments, the receiver candetermine that a particular segment, namely a segment with a sequencenumber between the last good segment and the next good segment ismissing. The receiver then can explicitly request retransmission of thebad segment by sequence number. This so-called selective reject featurepermits both the receiver and the transmitter to know the number offrames received in error from the tally of selectively rejectedsegments.

From the count of the number of frames sent and the number of selectivereject orders received over a given radio channel, the transmitter canthen dynamically adjust the size of later transmitted segments for thatchannel. Preferably, the segment size is adjusted based upon a formulathat depends upon the ratio of total number of data bits transferred tothe number of bits successfully used to carry information.

By performing forward error correction on a group of segments, ratherthan on individual segments, the channel bandwidth allocations can thusremain optimized.

The invention is particularly advantageous in an environment whichrequires the use of packet-oriented protocols such as TCP/IP. Becausethe number of channels needed to carry a single data stream can bevaried efficiently, burst rates can also be efficiently adapted.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis being instead placed upon illustratingthe principles of the invention.

FIG. 1 is a block diagram of a system in which a portable dataprocessing device uses a protocol converter according to the inventionto connect to a network.

FIG. 2 is a more detailed diagramming depicting the architecture of theprotocol converter and multichannel transceiver.

FIG. 3 is a diagram illustrating how network layer frames are dividedinto segments by a protocol converter located at a transmitter.

FIG. 4 is a detailed diagram of an individual segment and how multiplesegments are assembled into a forward error correction block.

FIG. 5 is a diagram illustrating how a protocol converter at a receiverreassembles the network layer frames.

FIG. 6 is a series of steps performed by a protocol converter located atthe transmitter to implement the invention.

FIG. 7 is a continuation of the diagram of FIG. 6.

FIG. 8 is a diagram of the steps performed by a protocol converterlocated at a receiver to implement the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Turning attention now to the drawings more particularly, FIG. 1 is ablock diagram of a system 10 for providing high speed data communicationservice according to the invention. The system 10 consists of a remotesubscriber unit 20, multiple bidirectional communication links 30, and alocal or service provider unit 40.

The subscriber unit connects to terminal equipment 12, such as aportable or laptop computer, hand held personal digital assistant (PDA),or the like. The subscriber unit 20 includes a protocol converter 25which in turn provides data to a multichannel digital transceiver 26 andantenna 27.

The protocol converter 25 receives data from the computer 20, andtogether with appropriate hardware and/or software, converts it to aformat suitable for transmission such as in accordance with knowncommunication standards.

The protocol converter 25 implements an intermediate protocol layer thatcoverts the data to a format appropriate for use by the multichanneltransceiver 26 according to the invention. As will be described in muchgrater detail below, at a network layer, the data provided by theprotocol converter 25 is preferably formatted in a manner consistentwith suitable network communication protocols, such as TCP/IP, to permitthe terminal equipment 12 to connect to other computers over networkssuch as the Internet. This description of the protocol converter 25 andprotocols is exemplary only and it should be understood that othernetwork layer protocols can be used.

The multichannel digital transceiver 26 provides access to one or morephysical communication links such as the illustrated radio channels 30.The physical links are preferably further encoded using known digitalmultiplexing techniques such as Code Division Multiple Access (CDMA) toprovide multiple traffic on a given radio channel 30 or sub-channels 31.It should be understood that other wireless communication protocols mayalso be used to advantage with the invention.

The communications channels may be implemented by providing multiplecoded sub-channels 31 on a single wide bandwidth CDMA carrier channel 30such as having a 1.25 MegaHertz bandwidth. The individual channels arethen defined by unique CDMA codes. Alternatively, the multiple channels31 may be provided by single channel physical communication media suchas provided by other wireless communication protocols. What is importantis that the sub-channels 31 may be adversely effected by significant biterror rates that are unique to each radio channel 30.

The service provider equipment 40 includes an antenna 42, a multichanneltransceiver 46, a protocol converter 45, and other interface equipment48 such as modems, bridges, gateways, routers, and the like, which areneeded to provide connections to the Internet 49 or other network.

At the service provider 40, the multichannel transceiver 46 providesfunctions analogous to the multichannel transceiver 26 of the subscriberunit, but in an inverse fashion. The same is true of the protocolconverter 45, that is, it provides inverse functionality to the protocolconverter 25 in the subscriber unit 20. Data is accepted from theprotocol converter 45 in the TCP/IP frame format and then communicatedto the Internet 49. It should be understood that the configuration ofthe remaining equipment 40 may take any number of forms such as a localarea networks, multiple dial up connections, T1 carrier connectionequipment, or other high speed communication links to the Internet 49.

Turning attention now to the protocol converters 25 and 45 moreparticularly, they provide bandwidth management functionality 29implemented between a physical layer such as provided by the CDMAprotocol in use with the multichannel transceivers 26 and a networklayer protocol such as TCP/IP providing connections between the terminalequipment 22 and the network 49.

The bandwidth management function 29 performs a number of tasks in orderto keep both the physical layer and network layer connections properlymaintained over multiple communication links 30. For example, certainphysical layer connections may expect to receive a continuous stream ofsynchronous data bits regardless of whether terminal equipment at eitherend actually has data to transmit. Such functions may also include rateadaption, bonding of multiple channels an the links, spoofing, radiochannel setup and teardown. The details for implementing a protocolconverter specifically for ISDN terminal equipment 22 and Code DivisionMultiple Access (CDMA) modulation techniques in use by the multichanneltransceiver 26 are more specifically described in a pending patentapplication by Thomas E. Gorsuch and Carlo Amalfitano, entitled “AProtocol Conversion and Bandwidth Reduction Technique Providing MultiplenB+D ISDN Basic Rate Interface Links Over A Wireless Code DivisionMultiple Access Communication System,” filed Dec. 17, 1997 and givenSer. No. 08/992,759, which is assigned to Tantivy Communications, Inc.,the assignee of the present application, and which application is herebyincorporated by reference.

The present invention is more particularly concerned with the techniquesused by the protocol converters 25 and 45 for formatting the data to betransmitted over implementing multiple logical sub-channels 31-1, 31-2,. . . , 31-n each of the multiple radio channels 30 in order to improvethe effective throughput rate between a transmitter and a receiver in abit error rate prone environment. It should be understood in thefollowing discussion that the connections discussed herein arebidirectional, and that a “transmitter” may either be the subscriberunit 22 or the service provider unit 40.

In addition, an “error” as described herein is a bit error perceived atthe higher layer such as the network layer. The invention only strivesto improve the overall system level bit error rate, and does not attemptto guarantee absolute data integrity.

Turning attention now to FIG. 2, there is shown in more detail a blockdiagram of a forward link and reverse link implemented according to theinvention, more particularly showing the protocol converter 25 andmultichannel transceiver 26 associated with the subscriber side unit andthe multichannel transceiver 46 and protocol converter 44 associatedwith the service provider unit 40.

Beginning with the lower portion of the diagram in the reverse linkdirection, that is, in the direction of transmission from the subscriberunit 20 to the service provider unit 40, the reverse link protocolconverter 25 consists of a buffer 61, segment framer 62, and forwarderror correction (FEC) unit 63. The multichannel transceiver 26 consistsof a pseudonoise (PN) code generator 64, modulator 65, and radiofrequency (RF) up converter 66. The buffer 61 receives input data in amanner which will be described in more detail further. Segment framer 62arranges data received from the buffer in an appropriate format to befed to the FEC unit 63. The FEC unit 63 applies a forward errorcorrection algorithm to the data using a known error correctiontechnique such as Reed Solomon, Turbo Codes, or other codes.

The transceiver 66, in this instance using it as a transmitter, spreadsthe resulting data by the PN sequence, modulates the PN spread data withappropriate channel coding per the assigned sub-channels 31, and the upconverts the result to the desired radio frequency.

On the receive side of the reverse link, that is, at the serviceprovider 40 side, the transceiver 44 performs a receiver function. Inthis instance, the RF down converter 71 feeds multiple receiving unitsthat each include an equalizer 72, a PN code despreader 73, anddemodulator 74. Each demodulated output is provided to a protocolconverter block that includes an FEC decoder 75, an inverse segmentframer 76, and buffer 77. A controller 78 may be used to control and/orimplement each of the protocol converter functions as described infurther detail below.

In the preferred embodiment, the FEC decoder 75 makes use of a so-calledtrellis decoder. Because a trellis decoder is a type of decoder whichcompares multiple bits in groups to arrive at an estimate of the correctreceived bits, when a trellis decoder does produce errors, they tend tooccur in groups.

The analogous functions are provided on the forward link. In thisinstance, the protocol converter 45 receives input data, processing itthrough a buffer 61, segment framer 62, and FEC unit 63. The transceiver46 performs a transmitting function over multiple sub-channels 31,including multiple spreaders 64, modulators 65, and RF up converters 66.

On the receiver side of the forward link, the inverse process isprovided by an RF down converter 71, equalizer 72, despreader 73, andchannel separator 79 and demodulator 74 for each channel. Forward errorcorrection unit 75, segment framer 76, and buffer 77 complete theimplementation of the protocol converter 25.

Turning attention now more particularly to FIG. 3, the operations of anexemplary protocol converter 25, at the transmit side will brieflydescribed. As shown, an input frame 80 as received from the networklayer is relatively large, such as for example 1480 bits long, in thecase of the TCP/IP protocol.

The input frame 80 is first divided into a set of smaller pieces orsegments 81-1, 81-2. The size of the individual segments 81 are chosenbased upon an optimum segment length determined for each of the channels30. For example, a bandwidth management function may make only a certainnumber of sub-channels 31 available at any time. A subset of theavailable sub-channels 31 is selected, and then the optimum number ofbits for each segment intended to be transmitted over respective one ofthe sub-channels, is then chosen. Thus as illustrated in the figure, agiven frame 80 may be divided into segments associated with foursub-channels 31. At a later time, there may be nine sub-channels 31available for a frame, with different optimum segment sizes for thesegment 81-2.

An optimum subframe size can thus be determined for each channel 30 forthese parameters described in our previously referenced co-pendingpatent application. In the preferred embodiment, for example, this isset equal to

$X = {{- H} + \sqrt{\left( {X_{current} + H_{current}} \right) \times \frac{H}{R}}}$

where H is the frame overhead in bytes, including any shared framesynchronization flags (7 e) between subframes, X_(c) is a current numberof data bytes assigned to a subframe, H_(c) is the current frameoverhead, and R is the observed subframe error ratio.

In the preferred embodiment, the segment size is the same for segments81 associated with each associated radio channel 30 and frame 80 tominimize overhead, although that is not an absolute requirement.

After the frame 80 is divided into segments 81, each of the segments 81has additional information appended to it. For example, each of thesegments 81 consists of at least a position identifier 82 a and anintegrity check sum such as in the form of a cyclic redundancy check(CRC) 82 b. Position identifier 82 a serves to indicate the position ofeach segment 81 within its associated large frame 80. The integritycheck sum 82 b serves to permit the receiver to determine whetherparticular segments 81 are received in error.

The segments 81 are then further prepared for transmission over eachsub-channel 31. In particular, the segments 81 are next grouped intoblocks 86. The number of segments in each block 86 is selected to aconvenient number depending upon the forward error correction 63, 75 tobe applied. For example, in a preferred embodiment, forward errorcorrection block 86 consists of a sufficient number of segments 81 tototal 1331 bits. If the FEC algorithm being applied is a one-third ratecode, this results in a FEC block 86 length of 4096 bits. Finally, theFEC block 86 is divided among the sub-channels 31 allocated to theparticular connection and transmitted.

FIG. 4 is a more detailed view of the format of a segment 81. Segment 81consists of a number of fields, including the position field 82 a andthe CRC field 82 b previously mentioned. A number of other fields arealso evident in the exemplary segment 81. In particular, there is a datafield 82 c which carries the associated source data taken from the inputlarge frame 80. This data field 82 c is a variable size and can bechanged according to optimized parameters as specified by an observederror rate. In a preferred embodiment, the number of data bits may varyfrom 2 up to 512 in a given segment 81 depending upon observed errorrates. As previously mentioned, all segments across a given input frame80 are selected to be equal in size, e.g., they have an equal sized datafield 82 c.

Furthermore, while a given input frame will be transmitted over multiplesub-channels 31, it will only be divided into segments which are to betransmitted over a given radio channel 30.

In addition, a frame offset field 82 d may be used to identify which ofa number of frames each segment 81 pertains to. This frame offset fieldis of particular use because of latencies involved in the system. Inparticular, segments 81 are not necessarily guaranteed to arrive at thereceiver in the same order as they were transmitted. Furthermore, ifparticular segments 81 are received in error, it may be necessary torequest retransmission. Therefore, it is possible that segments 81associated with more than one block need to be operated upon at thereceiver at a given time. The frame offset field 82 d therefore permitsthe receiver to distinguish which large frame 80 each segment 81 belongsto.

A code sequence field 82 e may be used to identify a sequence numberrelated to each sub-channel 31 at the beginning of each frame. Thispermits lower order channel processing to route segments 81 moreefficiently.

Finally, a message data field 82 f may be used to indicate whether thesegment 81 contains source data, i.e., active traffic data, or controlinformation for the intended recipient.

FIG. 5 illustrates the operations performed at the receiver side. Databits received from the multiple sub-channels 31 are first collected inorder to reconstruct the FEC block 86.

Next, the FEC algorithm is applied to detect and correct one or morebits using error correction coding. The resulting information is splitinto segments 81 using the known segment size. The segments 81 are thenexamined and the position field 82 is used to reconstruct the largeframe 80. Any segments 81 that are missing can thus be detected bycomparing the received position fields 82 a. If a sequence positionfield in a frame in a particular position or particular sequence number82 e is missing, it is assumed that the associated segment 81 was notreceived. It should be understood that appropriate buffering of data andsegments 81 is typically required in order to properly receive thesegments 81 and determine if any are missing. The buffer size willdepend upon the transmission rates, number of sub-channels 31, andpropagation delays in effect.

Upon detection of a missing segment 81, retransmission of the missingsegment 81 is requested by the receiver. At this point, the transmitterre-performs transmission of the missing segment 81. Once all of thesegments 81 in a particular large frame 80 are received, the positioninformation 82 a can then be used to arrange the data from the segments81 in the proper order to reconstruct the original large frame 80.

At this point, if any piece of the large frame 80 is still missing suchas when an end of frame command is encountered, retransmission of thecorresponding segment 81 can be requested at the indicated position,specifying a length for the missing piece.

Because of the use of both the position field 82 a and sequence field 82e, both the transmitter and receiver know the ratio of the number ofsubframes 81 received with errors to the number of subframes 81 receivedwithout errors. Also, the receiver and transmitter know the averagesubframe length for each channel.

FIG. 6 is a detailed flow diagram of a set of operations performed bythe transmitter in order to implement the invention. In a first state100, the large frame 80 is obtained from an upper communication layersuch as the network layer. In a next state 102, the transmitter computesan optimum segment size from past observations of frame error rates onthe individual sub-channels 81, preferably calculating an optimumsegment size for all communication channels available.

In a next state 104, the network layer frame 80 is divided into anappropriate number of segments 81 according to the optimum size for eachassociated sub-channel available. This division is also based upon theavailable sub-channel estimated throughput. A list of segments is thencreated.

In a next state 106, a position identifier and a cyclic redundancy check(CRC) code is added to each segment 81. The position identifier offsetwithin the large frame 80, as described above, is then added to allowcorrect positioning of the segment 81 when reconstructing the frame 80at the receiver end.

Next, an FEC block 86 is assembled from the multiple segments 81.Following that, in state 108, the FEC block 86 is demultiplexed and thebits in the FEC block are assigned to respective ones of the multiplesub-channels 31.

When the transmitter receives a retransmission request for a segment 81missing at the receiver, a state 110 is entered in which an optimumsegment size is computed from the observed frame averages for theavailable communications sub-channels 31. The segment list is then usedto requeue the segment for retransmission in state 112. Processing thencontinues at state 108 for retransmission of the missing segment 81.

FIG. 7 shows the remainder of the steps performed at the transmitter. Ina state 114, a channel-related sequence number is added to each segment81. In a next state 116, segment separators such as flags in the form“7E” are inserted into the segments. In addition, any zero insertionsuch as mandatory setting of a data bit to a 1 after a sequence of fivezeros, is performed. Other synchronization, separation, and codingtechniques may require that bits be inserted into the segments 81 atthis point. For example, a given channel 30 may make use ofconvolutional coding as specified by the IS-95 standard, and if so, thisis performed here.

In a next state 118, the segments 81 are sent over the availablechannels 31. Non-data frames such as logical start, logical end andother control frames may be inserted at this point as well.

In a final state 120, the transmitter operates on any segmentretransmission requests or positive acknowledgments of a large framebeing received correctly. Another frame transmission may be initiated,for example, at this point before completion of a frame in transit.

FIG. 8 shows a detailed sequence of the steps performed at the receiver.In a first state 200, a received FEC frame 86 is assembled from the bitstreams taken from multiple sub-channels 31. In the next state 201, theFEC frame is then split into segments 81 according to the currentsegment size.

In the next state 202, the subframes 81 are examined. Any segment with agood CRC is passed to the next following state 203. Any other receivedsegment 81 with a bad CRC is discarded.

Continuing with state 203, the receiver determines any missing sequencenumbers. The receiver then requests retransmission of segments 81 forthe missing pieces based upon sequence number by sending back aretransmission request to the transmitter.

In a next state 204, from the position identifier and the known lengthof each original large frame 80, the receiver attempts to rebuild theoriginal frame 80. In state 206, if any pieces of the frame 80 are stillmissing after the retransmission requests are all processed,accommodating the fact that a retransmission request itself may be lost,the receiver requests the missing portion of the large frame 80 byposition and size.

In state 208, once the frame 80 is completely received, a positiveacknowledgment is returned back to the transmitter.

It can now be understood that by applying the sub-channel segmentationstep first, prior to error correction encoding, the full benefit of theerror correction code is obtained while minimizing the amount of datathat needs to be re-transmitted. In particular, because bit errors inthe output of the trellis-implemented FEC decoder 75 tend to occurtogether, they will also therefore tend to affect a single segment 81.

EQUIVALENTS

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims. Those skilled in the artwill recognize or be able to ascertain using no more than routineexperimentation, many equivalents to the specific embodiments of theinvention described specifically herein. Such equivalents are intendedto be encompassed in the scope of the claims.

What is claimed is:
 1. A code division multiple access (CDMA) subscriberunit comprising: a protocol device, operatively coupled to a transceiverand an antenna, configured to produce packets and to segment the packetsto produce a plurality of segments, wherein each segment includes afirst field, a second field and a third field, wherein the first fieldincludes an indication of whether the third field includes control ortraffic data, the second field includes a sequence number of thesegment, and the third field is a data field including data of thepacket; the protocol device is further configured to combine segments ofthe plurality of segments into a block and to forward error correction(FEC) code the block; the protocol device is further configured tospread the FEC coded block using at least one CDMA code; and thetransceiver and antenna are configured to transmit the spread FEC codedblock.
 2. The CDMA subscriber unit of claim 1, wherein the FEC codeapplied to the block is a turbo code.
 3. The CDMA subscriber unit ofclaim 1, wherein the transceiver and the protocol device are furtherconfigured to receive information indicating a missing segment and toretransmit the missing segment.
 4. The CDMA subscriber unit of claim 1,wherein the protocol device is further configured to determine abandwidth to transmit the data and a number of codes associated with thedetermined bandwidth.
 5. The CDMA subscriber unit of claim 1, whereinthe packet is a Transmission Control Protocol/Internet Protocol (TCP/IP)packet.
 6. The CDMA subscriber unit of claim 1, wherein the spread FECcoded block is associated with a high speed data service.
 7. Thesubscriber unit of claim 1, wherein a number of CDMA codes to spread theFEC coded block is dynamically selected.
 8. A method comprising:producing, by a code division multiple access (CDMA) subscriber unit,packets; segmenting, by the CDMA subscriber unit, the packets to producea plurality of segments, wherein each segment includes a first field, asecond field and a third field, wherein the first field includes anindication of whether the third field includes control or traffic data,the second field includes a sequence number of the segment, and thethird field is a data field including data of the packet; combiningsegments of the plurality of segments into a block and forward errorcorrection (FEC) coding the block; spreading the FEC coded block usingat least one CDMA code; and transmitting the spread FEC coded block. 9.The method of claim 8, wherein the FEC code applied to the block is aturbo code.
 10. The method of claim 8, further comprising receiving, bythe CDMA subscriber unit, information indicating a missing segment andretransmitting by the CDMA subscriber unit the missing segment.